The present invention relates to a technique for enabling communication with a desired party user even when one of users at a plurality of communication terminals connected in a communication system does not know the terminal address of the communication terminal of the desired party user uniquely allocated thereto.
A communication system having communication terminals connected therein is generally designed so that one of users at the communication terminals can signal to or communicate with the communication terminal of a desired party user on the basis of a terminal address of the party user's communication terminal uniquely allocated thereto. Therefore, it is impossible for a caller to communicate with such a communication terminal that the caller does not know the party's terminal address.
In many of such communication systems, for the purpose of saving the number of terminal addresses as a limited resource, a terminal address is dynamically allocated to its communication terminal participating in the system when the communication terminal was connected to the system. For example, in the Internet, communication terminals being always connected via private line to the Internet are previously allocated their static terminal addresses (which are called "IP addresses" in the Internet), whereas communication terminals to be connected as necessary to the Internet via a public telephone line network (which connection is called "dial-up IP connection") are dynamically allocated their IP addresses when they are actually connected thereto.
In this way, in such a communication system that the communication terminal of a target party user is to be dynamically allocated its terminal address only when the terminal was connected; the communication terminal of the party user is not allocated when not connected to the system, while the party terminal address is being allocated thereto during the connection of the party terminal. However, the prior art communication system has had a problem that since the terminal address to be allocated varies each time its connection is carried out, it is difficult to communicate with such a party user communication terminal.
In order to facilitate communication between the users of the communication terminals, there has conventionally been suggested such a communication system that a monitor server for monitoring communication terminals being connected is provided, as disclosed in a journal entitled "COMMUNICATIONS OF THE ACM", an article entitled "Net. Speech: Desktop Audio Comes to the Net", Vol. 38, No. 10, October 1995.
In such a communication system as disclosed in the above literature, more specifically, a user sitting at one of the communication terminals, when he wants to connect its own terminal to the system, first declares its connection by informing the monitor server of his user name, in such a manner that the monitor server manages the user names informed by all the communication terminals of such users' who declared their connection as well as the terminal addresses allocated to the communication terminals. And the user of the communication terminal acquires a list of all user names under management of the monitor server. When the user informs the monitor server of the desired party user by selecting the desired user from the acquired user name list to specify the party user, this causes monitor server to call the communication terminal of the party user on the basis of the terminal address corresponding to the informed user name.
With such an arrangement as mentioned above, even when a user sitting at one of the communication terminals does not know the terminal address assigned to the communication terminal of the party user, he can communicate with the party user.
In such a communication system as disclosed in the above literature, however, the user of the communication terminal can call any one of the communication terminals being connected to the system through intervention of the monitor server, but to the contrary, may be called by all the communication terminals being connected thereto, which means that the caller communication terminal must also respond to the calls troublesomely by the communication terminals with which he does not want to communicate.
The above communication system is also disadvantageous in that the user of the caller communication terminal may be called by all the communication terminals even during communication with other communication terminal user, thus hindering its smooth communication.
Another disadvantage of the communication system is that the caller user of the communication terminal, when wanting to specify the user name of a desired party user from the user name list acquired from the monitor server, must troublesomely find the party user name from a lot of user names managed by the monitor server.
Yet another disadvantage of the system is that the caller communication terminal, which failed to inform the monitor server of its own party user name, cannot still be signaled by any other communication terminals so long as they does not know its terminal address, thus restricting the number of communicatable party users.